1. Field of the Invention
The present invention relates to a display device, and more particularly to a display device having a light-sensing function.
2. Discussion of the Background
Thin and light display devices are required to meet the recent demand for lighter and thinner personal computers and televisions. Thus, the bulkier and heavier cathode ray tubes (CRTs) are being replaced with flat panel display devices.
Examples of flat panel display devices include a liquid crystal display (LCD) device, a field emission display (FED) device, an organic light emitting diode (OLED) display, and a plasma display device (PDP).
Generally, an active flat panel display includes a plurality of pixels arranged in a matrix, and a pixel's light intensity is controlled on the basis of predetermined luminance information to display images. Among active flat panel displays, an OLED display is a self-emissive display device in which fluorescent organic materials are electrically excited to display images. Further, the OLED display has low power consumption, wide viewing angle, and high pixel response speed. Accordingly, the OLED display may be suitable for display of a high-definition motion picture.
Generally, the OLED display includes thin film transistors (TFT) controlling OLEDs. The TFTs may be polysilicon TFTs and amorphous silicon TFTs, depending on their active layer. Since OLED displays having polysilicon TFTs have various merits, they are widely used. However, since manufacturing polysilicon TFTs may be complicated, the display may be expensive to fabricate. Further, it may be difficult to obtain a large screen when using the OLED display.
On the other hand, an OLED display using amorphous silicon TFTs may be suitable for obtaining a large screen, and it may be manufactured by fewer manufacturing processes than an OLED display using polysilicon TFTs. However, when a positive DC voltage is continuously applied to a control terminal of the amorphous silicon TFT, a threshold voltage of the TFT changes. Hence, even when a uniform control voltage is applied to the TFT, a non-uniform current may flow in the OLED. Consequently, the luminance of the OLED display may be reduced, thereby causing image degradation. This eventually results in a reduced life span of the OLED display.
Therefore, various pixel circuits have been proposed to prevent image degradation by compensating for the variation of TFT threshold voltage. However, most pixel circuits include a plurality of TFTs, capacitors, and wiring. Accordingly, most pixel circuits have pixels with low aperture ratios.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.